Greater Sage-grouse Linkage Pinch-points in the SageCon study area, southeastern and central Oregon

This dataset, included in the Oregon Decision Support System for Sagebrush Steppe (ORDSS), is a component of habitat connectivity analyses for Greater Sage-grouse (GSG) in southeastern and central Oregon conducted in 2014 in accord with the Sage Grouse Conservation Partnership (SageCon) by The Nature Conservancy in Oregon (TNC). Covering the full extent of linkage zones defined by the mapped normalized least-cost paths (NLCCs), the surface identifies ‘pinch-points’ between pairs of 'lek kernels' (see Jones et al. 2015, below). Pinch-points are areas within which connectivity could be severed with the loss of a relatively small amount of dispersal habitat.

The surface was produced using the open source Circuitscape program (McRae and Shah 2009) as called from the Pinchpoint Mapper tool in the Linkage Mapper toolbox (McRae and Kavanagh 2011). Circuitscape uses circuit theory –a branch of graph theory with a lexicon and algorithms specific to analysis of electrical circuit topologies –to model habitat connectivity across landscape mosaics. With the study landscape represented as a conductive surface, metrics including ‘effective resistance’, current flow, and voltage can be calculated to represent ecological processes such as individual species movement or gene flow across a metapopulation. In kind with graph theory more broadly, the circuit theoretic framework supports concurrent analysis of not only multiple but all possible species movement routes across a landscape (McRae and Shah 2009).
For each linkage in this study, current was applied between the associated pair of lek kernels. The current was run over squared resistance values to increase contrast in the resistance raster, and flow for each linkage zone was limited to areas below the same CWD distance threshold (10 cw-km) used to map the NLCCs. Locations of highly constricted and thus strong current flow are identified as ‘pinch-points’. Given the lower incidence or absence of alternative movement routes around such ‘bottlenecks’, habitat degradation and/or loss within them will, by unit area affected, entail a disproportionate adverse effect on connectivity. At a landscape scale, ‘pinch-points’are the areas at which linkages are most susceptible to being severed and which may deserve prioritization for habitat protection.
For prescriptively symbolized linkage zones, see 'SageGrouseConnectivity_LinkageZones.lyr' and for pinchpoints, see 'SageGrouseConnectivity_Pinchpoints.lyr'. 
For more details, see: Jones et al (2015), below.

The Nature Conservancy in Oregon

Jones, A., M. Schindel and S. Scott. 2015. Mapping Habitat Connectivity for Greater Sage-Grouse in Oregon’s Sage-Grouse Conservation Partnership (SageCon) Assessment Area. Produced by The Nature Conservancy (Portland OR) in partial fulfillment of BLM Cooperative Agreement L12AC20615. Available online: DOI: 10.13140/RG.2.2.22266.08640.

McRae, B.H. 2012. Pinch-point Mapper Connectivity Analysis Software. The Nature Conservancy, Seattle WA. Available at: www.circuitscape.org/linkagemapper

McRae, B.H. and D.M. Kavanagh. 2011. Linkage Mapper Connectivity Analysis Software. The Nature Conservancy, Seattle WA. Available at: www.circuitscape.org/linkagemapper

McRae, B.H., and V.B. Shah. 2009. Circuitscape user’s guide. The University of California, Santa Barbara. Available at: www.circuitscape.org

The Nature Conservancy shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any sale, distribution, loan, or offering for use of these digital data, in whole or in part, is prohibited without the approval of the Nature Conservancy. The use of these data to produce other GIS products and services with the intent to sell for a profit is prohibited without the written consent of the Nature Conservancy. All parties receiving these data must be informed of these restrictions. The Nature Conservancy shall be acknowledged as data contributors to any reports or other products derived from these data.